1. Technical Field
The present invention relates to an optical information processing apparatus and an optical information processing method, and more particularly, to an optical information processing apparatus and an optical information processing method of processing optical information by using two or more multiplexing recording methods.
2. Related Art
As an example of an optical data processing apparatus, a holographic optical information processing apparatus records interference fringe formed by intersection of two beams in a storage medium. The interference fringe is a kind of recording data. One of the two beams is an optical modulated signal beam, and the other is a reference beam having the same wavelength as that of the signal beam. The holographic optical information processing apparatus reproduces the data by irradiating the reference beam to the interference fringe formed on the storage medium and detecting a readout beam generated by diffraction of the interference fringe.
The holographic optical information processing apparatus may use various multiplexing methods in order to increase recording capacity thereof.
As examples of the multiplexing methods, there are an angular multiplexing method, a phase-code multiplexing method, a wavelength multiplexing method, a shift multiplexing method, a peristrophic multiplexing method, a correlation multiplexing method, a fractal multiplexing method, and the like.
In addition, there are techniques using a combination of two or more multiplexing methods. As an example of the techniques using a combination of the multiplexing methods, there is a polytopic multiplexing method.
For example, a polytopic multiplexing method is disclosed in U.S. Pat. No. 7,092,133, titled “Polytopic multiplex holography” issued to Kenneth, et al. In addition, a polytopic multiplexing method is disclosed in an article, titled “Polytopic multiplexing” by Anderson, Ken; Curtis, Kevin (Optics letters, Volume 29, Issue 12, pp. 1402-1404, June, 2004).
In the polytopic multiplexing method proposed by Kenneth, et al., adjacent hologram stacks on a storage medium are subject to a partial spatial overlapping process so to multiplexing-recording optical information on the hologram stacks. In the proposed multiplexing method, it is disclosed that the optical information may be multiplexing-recorded on the hologram stacks by using any one of angular, wavelength, phase code, peristrophic, correlation and fractal multiplexing methods.
On the other hand, if diffraction efficiency of holograms which are overlapped and recorded by using a multiplexing method is not uniform, optical information reproducing efficiency may deteriorates. Therefore, the holograms which are recorded in a storage medium by using the multiplexing method requires for good and uniform diffraction efficiency at the time of reproducing of the holograms. However, in most of conventional multiplexing methods for multiplexing recording holograms, only the solution for increasing a recording density is proposed, but the diffraction efficiency at the time of reproducing of the holograms is not taken into consideration.